Switching apparatus



June 10, 1958 E. G. HILLS ETAL.

SWITCHING APPARATUS 2 Sheets-Sheet 1 Filed Feb. 25, 1954 J9 19g/@gewi 727m, Wm, wm; ww

June 10, 1958 IE. G. HILLS ET A1.

SWITCHING APPARATUS 2 Sheets-Sheet 2 Filed Feb. 25, 1954 United States Patent O SWITCHING APPARATUS Elmer Guy Hills, Des Plaines, and Elmer S. Hewitt, Wilmette, Ill.

Application February 2S, 1954, Serial No. 412,489

3 Claims. (Cl. 20G-33) This invention relates generally to switching apparatus and, more particularly, to a new and improved timing switch and associated actuating mechanism for delivering a uniform force to actuate the switch.

The switching apparatus of the present invention is particularly adapted for use in energizing and de-energizing the electrical control circuits for a hand drying mechanism, although it will be understood that the apparatus is not limited to such use. However, since operation of the apparatus in conjunction with electrically operated hand driers affords an excellent illustration of most of its features, the ensuing description will be concerned primarily therewith. One of the principal requirements for switching apparatus for hand driers is that suitable contacts must be closed immediately upon the actuation of the switch by the operator and these contacts must remain closed for a predetermined interval while the drying operation is performed. Prior arrangements for meeting this requirement have generally involved elaborate relay holding circuits of the mechanical or electromagnetic type which have been both space-consuming and expensive.

At present, hand drying mechanisms are principally used in public establishments where they are operated by any number of persons who apply widely divergent degrees of force to the manually actuated switch control element. Since repeated applications of force of excessive magnitude to the switching mechanism controlled by the'manually actuated element would cause damage to the switch to appreciably shorten its life, it is desirable to apply a uniform force to this mechanism regardless of the force applied to the manually actuated element.

It is an object of the present invention, therefore, to provide new and improved switching apparatus which obviates all of the aforementioned difiiculties.

Another object of the invention is to provide a simply constructed, inexpensive, yet efficiently operating switching apparatus which is sufficiently rugged to withstand a relatively long period of hard use.

A further and more specific object of the invention is to provide manually operable switching apparatus including means for applying a uniform force to actuate the switch of a magnitude which is independent of the degree of force applied to the manually operated elements of the mechanism.

A still further object of the invention is to provide ya manually actuated switch for -instantly closing its contacts when actuated, and for maintaining its contacts closed for a predetermined interval measured by the passage of iluid through a restricted passageway.

The invention both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which:

Fig. 1 is a front elevational view partly in section showing a switching apparatus characterized by the features of the present invention;

Figs. 2 and 3 are partial views of the switching appalll ICC

ratus shown in Fig. l illustrating the position occupied by the various component elements of the mechanism during its manual actuation;

Fig. 4 is a vertical sectional view showing the switch portion of the apparatus of Fig. l;

Fig. 5 is a greatly magnified view of the constricted opening through which uid ilows to time the interval of contact closure in order to aid in explaining the present invention;

Fig. 6 is a vertical sectional view illustrating a second embodiment of the switch portion shown in Fig. 4;

Fig. 7 is a front elevational view partly broken away of a third embodiment of the switch portion shown in Fig. 4; and

Fig. 8 is a plan view of the switch portion shown in Fig. 7.

Referring now to the drawings, and more particularly to Figs. 1, 2 and 3 thereof, the present invention is there il-lustrated as embodied in a switching apparatus comprising a manually operable switch actuating mechanism, indicated generally as 10, and a switch or switch portion, generally indicated at 11, both of which are mounted upon a frame including a pair of substantially parallel at plates 12 and 13, which may be formed of metal, plastic, or any other suitable material. These plates are preferably maintained in spaced apart relationship by the insertion of four cylindrical spacers, all designated by the reference character 12a, and each mounted between adjacent corners of the opposed plates. As illustrated in Figs. l and 3, the component elements of the actuating mechanism 10 are supported upon one side of the plate 12, whereas the switch 11 is mounted in the space between the plates 12 and 13 on a shaft 14 extending horizontally through the plates and having one end protruding beyond the plate 12 in order to receive a gear 15, the purpose of which will be evident as the description proceeds.

For the purpose of actuating the switch 11, the mechfanism 10 includes a manually actuated reciprocable plunger 16 of any suitable cross section carrying a push button 17 on its free end and extending through a cooperating guide opening in a guide bar 18 suitably secured to the plate 12. In order to provide additional means for guiding the plunger 16 in its reciprocation from left to right and from right to left, as viewed in Figs. l, 2 and 3, the plate 12 also mounts an L-shaped guide 19 having a leg 19a in contact with the upper edge of the plunger 16.

In order to return the plunger 16 to its normal or deactuated position, as shown in Fig. l, after it has been manually moved to the right, as viewed in Figs. 2 and 3, by force applied to the push button 17, a suitable compression spring 20 encompasses the plunger and is held between the guide bar 18 and a spring retaining collar 22 carried by the plunger. The collar 18 is maintained in position on the plunger between one end of the spring 20 and a holding pin 23 inserted within a small aperture in the plunger. Thus, in the absence of pressure on the push button 17, the spring 20 urges the plunger 16 and the push button to the left, as viewed in the drawings, and holds them in the position shown in Fig. l.

To relate the plunger 16 to other elements of the switching apparatus of the present invention, the end of plunger 16 remote from knob or push button 17 may be bifurcated with the bifurcations 16a and 16b extending laterally away from plate 12 so as to define a slot or channel between the bifurcations. The bifurcations are preferably notched to further define a channel for receiving a reciprocable bar 24 which includes an end portion 24a extending laterally of the bar and having a suitable opening through which the plunger 16 passes. If a rectangular plunger 16 is employed, this opening will, of course, be rectangular. The bar 24 also includes a 3 portion 24h and a somewhat downwardly displaced p0rtion 24e, the junction of these two portions forming an upper abutment 24d which Vfunctions as a stop for limiting the movement in one direction of the plunger 16 in a manner to be more fully described hereinafter.

The lower edge of the portion 24b of the bar 24 is suitably indented to form a camming surface 24e for purposes which willbecome apparent from the ensumg description. The portion 24e of the bar 24 extends through a rectangularly-shaped opening in a guide flange 25 secured in any suitable manner to the plate 12. The end of the bar 24 remote from plunger 16 has pivotally mounted thereon a pawl 26. As illustrated, pawl 26 has a bifurcated end portion 26a fitting over the end of the bar in order to permit the pawl to pivot about a pivot pin 27 which may be threaded through aligned openings in the bifurcations so as to extend loosely through an opening in the end of the bar 24. Y

For the purpose of delivering a uniform force to the bar 24 when the plunger 16 is actuated, a spring 28 surrounds the bar and has its respective ends in engagement with the laterally extending bifurcations 16a and 16b on the plunger and with a spring retaining pin 29 inserted within an appropriate aperture in the bar 24. Actually, a plurality of aligned and spaced apertures, all indicated by the reference character 30, are provided in the bar in order to provide a means for adjusting the amount of compression of the spring 28, thereby to control the magnitude of the uniform force delivered to the bar 24.

From the above description it will be apparent that the plunger 16 and bar 24 together provide a telescoping force transmitting member for delivering a uniform force determined by the Venergy stored in spring 2S to a mechanism to be actuated regardless of the force applied to plunger 16.

In order to retain the bar in position to permit the spring 28 to be compressed upon actuation of the plunger 16, there is provided a latch 31 mounted for limited pivotal movement about a stub shaft or pivot on the plate 12 and having a retaining lip or latching portion 31a in engagement with the pawl 26. To provide for the release of the pawl 26 from latching portion 31a of the latch 31 only after the spring 28 has been fully compressed, the latch 31 includes a detent 32 which cooperates with a slot 33 in the lower portion of the plunger to pivot the latch portion 31a out of engagement with the bar 24. When the latch 31 is disengaged from the pawl 26, the energy stored in the spring 28 is released to deliver a uniform force to the bar 24 due to the fact Vthat spring is always compressed by the same amount. The latch 31 also includes a support 31b for preventing the pawl 26 from pivoting in a clockwise direction as viewed in Fig. l of the drawings.

For the purpose of utilizing this uniform force to actuate a suitable mechanism such as the switch 11, the energy delivered to the bar 24 moves the bar and the pawl 26 to the right, as viewed in Fig. 1, and may be utilized to actuate any suitable mechanism. To convert reciprocal movement to rotary movement, the pawl 26 is caused to engage one end 34a of a rack 34 positioned in the path of movement of the pawl. To guide the reciprocal movement of the rack 34, it extends through suitable openings in guide flanges 37 and 38 formed on the plate 12, and meshes with the gear 15 on the switch shaft 14. Thus, when the pawl 26 engages the end 34a of the rack 34 and moves the rack to the right, as viewed in Fig. l, the shaft 14 is rotated Vthrough a predetermined angle, which, in order to illustrate the invention, will be assumed to be approximately 180. To provide for the disengagement of the pawl from the end 34a of the rack 34 after the shaft has been rotated through the desired angle, the rack is downwardly inclined so that as it moves to the right it also has a slight downward movement which eventually causes the end 34a to descend below the essentially straight path of movement of the pawl 26. Upon the latter occurrence the pawl disengages itself from the rack gear and the shaft returns to its normal position, as shown in Fig. 1, by any suitable means, such, for example, as by the action of gravity on the switch 11, as will become evident from the ensuing description. It will be understood that the mechanism thus far described, although admirably suited to actuate a switch, may be used to operate other devices requiring the application of a uniform force. Before describing the switch 11 in detail, it may be pointed out that the switch is mounted for pivotal movement with shaft 14, and such pivotal movement actuates the same.

From the foregoing explanation it will be understood that the switch 11 and its actuating mechanism 10 are both shown in Fig. 1 in their normal or deactivated positions prior to the application of manual force to the mechanism. ln order to actuate the switch, the operator presses on the push button 17 to move the plunger 16 from the position shown in Fig. l to that shown in Fig. 2. The movement of the plunger 16 compresses both of the springs 20 and 28, as shown in Fig. 2, since, during this movement of the plunger 16, the bar 24 remains stationary due to the fact that the pawl 26 remains in firm engagement with the lip or latching portion 31a of the latch 31. As soon as the plunger 16 occupies the position shown in Fig. 2, the detent 32 comes into alignment with the slot 33 in the lower edge of the plunger 16. The force of the compressed spring 28 against the lip 31a pivots the latch 31 about the shaft or pivot 35 and causes the detent 32 to move into engagement with the slot 33. Y As the latch 31 is pivoted about the shaft 35, the lip 31a moves out of engagement with the pawl 26 which is resting on support 31b, and the bar 24 is thus free to move to the right under the force produced by the energy stored in spring 28. The engagement of the detent 32 with the slot 33 prohibits further movement of the plunger 16 to the right, and thus the force delivered to the bar 24 is solely that which results when the stored energy in the spring 28 is released. Therefore, this force is uniform and its magnitude is independent of the pressure applied to the Aknob or push button 17, provided, of course, that such pressure is sufficient to move the plunger 16 the required distance to the right, as viewed in the drawings.

As the bar 24 moves to the right from the position shown in Fig. 2 due to the expansion of spring 28, the pawl 26 engages the end 34a of the rack 34'and induces the latter to rotate the gear 15 and the shaft 14. VThe rotation of the shaft 14 actuates the switch lil in a manner which will become evident from the ensuing description. By the time that the shaft 14 has been rotated through an angle suicient to actuate the switch 10, the inclined rack 34 has been moved both downward and to the right to the position shown in Fig. 3, at which time the end 34a of the rack 34 is moved out of engagement with the pawl 26. The movement of the bar 24 to the right also brings the camming surface 24e of the portion 24b of the bar 24 into engagement with the detent 32 resting within the slot 33. As the bar 24 is further moved to the right by expansion of spring 28, the camming surface 24e moves the detent out of the slot and pivots the latch 31 in a counterclockwise direction about the shaft 35 until it assumes the position shown in Fig. 3. The pawl is pivoted slightly about the axis of the screw 27 due to the engagement between the lower edge of the pawl and the upper edge of the lip 31a on the latch. With the detent 32 moved out of the slot 33 by the camming surface 24e, the plunger 16 is free to return to its normal position, and thus the energy stored in the spring 20 during the actuation of the mechanism, 10 is released to begin movement of the plunger 16 to the left from the position shown in Fig. 3i The plunger 16 moves to the left, asviewed in Fig. 3, under the force of spring 20 until the laterally extending bifurcation 16a on the end of the plunger 16 strikes the abutment 24d on the bar 24, thereby limiting the movement of the plunger 16 in this direction. After the lip 16a and the abutment 24d are in engagement, the plunger 16 and the bar 24 move in unison to their initial positions shown in Fig. 1 under the continued force exerted by spring 20. When the bar 24 reaches its initial position, shown in Fig. 1 of the drawings, the pawl 26 pivots slightly in a clockwise direction from the position shown in Fig. 3 due to the force of gravity on this member, thus bringing the free end of the pawl again into engagement with the lip 31a, as shown in Fig. 1. When this occurs, the switching mechanism is completely restored to its normal position in preparation for a subsequent application of pressure to the push button 17 in order to repeat the operation described above.

Since a mercury type switch is one readily operated to the closed or open position, the switch 11 has been indicated as a mercury switch, and the present invention is also concerned with certain features of the switch 11 apart from the mechanism 10 already described. Turning now to Fig. 4, there is shown the switch 11, illustrated as a mercury switch disposed in its open position, as also shown in Fig. 1 of the drawings. As illustrated, the switch 11 comprises an enclosed envelope or housing 40, preferably formed of glass or the like, and including i two parallel connected passageways comprising a large passageway 41 and a smaller passageway 42 including a restricted portion 42a, both of these passageways being joined at the bottom by a well 43 and at the top by an enlarged chamber 44. As bestl shown in Fig. l, the well 43 contains a pool of conducting uid 45, preferably of mercury, when the switch 11 is in its normal position prior to actuation of the mechanism 10. To complete the switch, a pair of xed contacts 46 and 47 extend through the wall of the housing 40 and into the enlarged chamber' the outer ends of these contacts being connected through leads 48 and 49 to' any electrical device or circuit to be controlled. For the purpose of preventing oxidation of the metal parts of the switch 10 upon the occurrence of switching arcs, the housing 40 may be filled with inert gas or reducing gas in addition to including the mercury 45.

To provide means for mounting the switch 11 between the parallel supporting plates 12 and 13 for pivotal movement with shaft 14, the housing 4l) is carried by a U- shaped channel piece having opposed sides t), only one of which is shown in Fig. 4, joined by a bottom plate 51 which extends only partly along the length of the sides 50 to provide an opening 51a. The portion of the housing 4d defining the enlarged chamber 44 rests on the bottom plate 51, while that portion of the housing 40 defining the passageways 41 and 42 and the well 43 extendsthrough the opening 51a and downwardly from the opposed sides 5t). in order to maintain the housing 40 in position yon the U-shaped channel piece, a pair of spaced retaining pins 52 and 53 extend between pairs of aligned openings in the opposed sides 50, each of these pins contacting the exterior wall of the housing 40. The shaft 14, which is rotated by the actuating mechanism 1t), extends through each of the opposed sides 56 in positive engagement therewith in order to cause rotation of the switch 11 with the shaft 14, as mentioned above.

When the shaft i4 is rotated through an angle of 180 in the manner previously described, the switch 11 is rotated in a clockwise direction untilit is inverted from the position shown in Figs. l and 4, at which time this switch occupies the position shown in Fig. 3. The clockwise rotation of the switch 11 is limited by a suitable stop 52 secured to the plate 13 and adapted to engage an edge of one of the sides Si? at the extremity of desired 6 movement of the switch. When the switch 11 is inverted, the pool of mercury 45 in the well 43 flows through the large passageway 41 into the enlarged chamber 44, which chamber at this time is located at the bottom of the switch. At the completion of the actuating stroke delivered to the shaft 14 by movement of the bar 24, the pawl 26 becomes disengaged from the rack 34 and the weight of the mercury causes the switch 11 to rotate in a counterclockwise direction and return to its normal position due to the effect of gravity. The counterclockwise rotation of the switch 11 is limited by a stop 53 secured between the plates 12 and 13, and preferably including suitable cushioning material 54 so that when the stop is contacted by the glass housing 40 damage will be avoided. The return of the switch to the position sh wn in Fig. 4 induces a counterclockwise rotation of the shaft 14 and at the same time restores the rack 34 to its normal position (Fig. l). The return of the switch 11 to this position has another very important result in that a portion of the pool of mercury is trapped within the enlarged chamber 44, as best shown in Fig. 4. This is because the connection with passageway 41 is defined by a passageway section 41a above the contacts 46 and 47, whereby the entrapped liquid covers the contacts 46 and 47, and thus closes the electrical circuit controlled by the contacts through the conductors 48 and 49. The mercury trapped in the chamber 44 can return to the chamber 45 only through passageway 42. Due to the fact that this passageway includes a constricted portion 42a providing a structure somewhat analogous to the well-known hour glass, the ow of mercury is impeded.

When the switch 11 returns to its normal position after actuation, the sudden deceleration of the mass of mercury induced by the impact of the glass envelope with the stop 53 increases the effective pressure head above the constriction 42a and starts the flow of mercury through the small opening. The mercury 45 in the upper chamber 44 is maintained in simultaneous contact with both of the fixed contacts 46 and 47 for the interval of time required for the ow through the constriction 42a to reduce the level of mercury in the upper chamber and break the contact. The length of this interval is a function of the rate of ow of the mercury, which in turn depends upon the size of the opening in the constricted portion 42a of the passageway 42.

To provide means for quickly moving the mercury away from the contact 46 to break sharply the electrical conducting path between the contacts 46 and 47, there is provided a barrier 56 of ceramic or the like having a liquid guiding trough 56a formed therein. The barrier 56 preferably rests upon the lower contact 47 and includes a small contact receiving well 56b into which the contact 46 extends. When the desired time interval has elapsed and the level of the mercury in the upper chamber has dropped to a point where its surface nearly touches the bottom of the trough 56a in the barrier at the point designated 56e in Fig. 4, the surface tension of the mercury causes a sudden parting of the surface into two portions, one of which is the main body of mercury in the upper chamber 44 and in the restricted passageway 42, and the other of which is a small drop of mercury in the well 5611 surrounding the lower end of the Contact 46. Obviously, when the surface of the mercury is broken into two parts, the electrical conducting path between the contacts 46 and 47 is-severed. After electrical contact is broken, the mercury continues to flow through the restricted passageway 42 until the entire mercury pool has again collected in the well 43 at the bottom of the housing, at which time the switch 11 is ready for the next succeeding actuation by the mechanism 10.

The operation of the constricted portion 55 of the passageway 42 in impeding the flow of mercury therethrough will be best understood by reference to Fig. 5, which is a greatly enlarged view of this constricted por- IOD. In order to insure that mercury trapped in the upper chamber 44 of the housing 40 upon actuation of the mechanism will begin to flow through passageway 42, it is necessary that the constricted portion 42a be properly tapered as indicated by the sloping side walls 55a and 55b in the greatly enlarged view of Fig. 5. Considering first a small quantity of mercury 60 having an upper surface 60a and a lower surface 60b, and adapted to pass through the small opening in the constricted portion 42a, it will be recognized that the surface of the mercury will contact the glass walls of the passageway at an angle indicated by the reference character A. The magnitude of this angle is a function of the characteristics of the mercury, and is thus constant for all bounding edges of the mercury in contact with the glass walls. Both the upper and lower surfaces of the mercury exert forces on the glass walls as a result of the surface tension of the mercury, the surface tension due to the upper surface 60a being directed downwardly in the direction of the arrow T2, and that due to the lower surface being exerted upwardly in the direction indicated by the arrow T1. The total upward force resulting from the surface tension of the lower surface 60b is equal to the length of the line of contact between the mercury and the glass multiplied by the surface tension of the mercury, the latter being a constant equal to 470 dynesV per centimeter. Thus, the total upward force may be expressed as:

where k is the surface tension constant of mercury, and R1 is the radius of the passageway at the lower surface 60b.

The upward pressure P1 resulting from this force is, of course, the total force divided by the area (1R12), and may be expressed as:

2k P1 Rl Thus, it can be seen that the pressure is inversely proportional to the radius. It, therefore, follows that the upward pressure exerted by the lower surface 60a exceeds the downward pressure resulting from the surface tension of the upper surface 60h due to the fact that the radius R2 of the upper surface is larger than the radius R1. Therefore, in order for mercury to begin to ow through the passageway 42, the pressure head, due to the weight of mercury in the column above the constricted portion 42a, must overcome the excess surface tension exerted by the lower surface. In the limiting casein which the mercury would just barely start to flow downward, the diierence between the pressures on the two surfaces would equal the pressure on the lower surface due to the head of the mercury h of Fig. 5. By so constructing the glass tube such that the change in tube radius for a given change in tube height is always less than a certain amount, the mercury will always flow through the tube under its own weight. Once the stream of mercury has started through the neck of the tube such that the lower surface area is increasing as the mercury moves downward, the'back pressure of the lower surface continually decreases and the mercury ows faster and faster. lf the tube is shaped such that its divergence is less rapid than given by the formula:

i R2* (MB1-isch) where all unknowns are in inches, then the mercury will always start through the opening.

From the foregoing explanation of the switch 11, it will now be apparent that when the switch is in its normal or quiescent condition, the pool of mercury 45 is collected in the well 43 at the bottom of the housing 40. Upon the Vactuation of the switch actuatingl me`chanism 10 in the manner previously described, the shaft 14 is rotated through an angle of 180 to invert the switch 11 and cause mercury to ilow through passageway 41 into the upper chamber 44. As previously described, the switch actuating mechanism 10 operates to withdraw the pawl 26 andthe bar 24 as'soon as its power stroke is delivered, with the result that the weight of the switch 11 causes rotation of the switch and the shaft 14 to return the switch to its normal position almost instantly. The mercury trapped in the chamber 44 closes the contacts 46 and 47 almost instantaneously with the actuation of the mechanism 10 and these contacts remain closed for a predetermined interval while the mercury flows slowly through the passageway 42. At the end of the predetermined interval, the length of which is determined by the size of the opening in the constricted portion 42a of the passageway 42, the level of the mercury in the upper chamber 44 is reduced so that the mercury no longer engages the contact 46 and the electrical circuit is broken.

It will now be appreciated that the uniform force de livered to the shaft 14- from the switch actuating mechanism 10 causes the switch 11 to rotate at the same rate and by the same amount regardless of the speed or force of operation of the push button 17. In this manner damage to Vthe glass housing is avoided and the timing cycle of the switch 11 is uniform in duration. Thus, when applied to a hand drying mechanism, the mechanism remains energized for the same predetermined length of time regardless of how the user actuates the push button 17. Obviously, the device of the present invention may be used for numerous timing operations and switching functions.

Instead of actuating the mercury switch through a complete cycle for every operation, a sort of double-ended device may be employed in which a half cycle is suilicient for one operation. Such an arrangement is disclosed in a second embodiment of the present invention, shown in Fig. 6, wherein there is shown a switch 62 which differs from the switch shown in Fig. 4 principally by the use of a second set of contacts and by the elimination of the enlarged passageway 41. Specifically, the switch illustrated in Fig. 6 comprises a housing 63 attached to a U-shaped channel 64 in any convenient manner, as by retaining pins 65 extending between opposed sides of the channel. The channel 64 is iixedly mounted in any suitable manner on a shaft 66 which functions to alternately invert the switch for purposes which will be evident hereinafter. The housing 63 includes a pair of enlarged chambers 67 and 68 interconnected by a passageway 69 having a constricted portion 69a therein for inhibiting the ow of a pool of mercury or other conducting iluid contained within the housing. Extending through the walls of the housing 63 and into each of the chambers 67 and 68 are two pairs of fixed contacts, the upper pair of contacts being designated as 70 and 71, and being connected through leads 72 and 73 to a device to be controlled. The lower set of contacts, designated 74 and 75, are also connected through leads 76 and 77 to a device to be controlled, which device, if desired, may be different from that controlled by contacts 70 and 71.

Barriers 79 and 80 of ceramic or the like,'which may be identical with the barrier 56 described above, are provided between the upper and lower pairs of contacts in order to provide for the rapid withdrawal of mercury from the upper contacts 70 and 71 in the manner heretofore described in conjunction with the description of the barrier 56. When the switch 62 is in its normal or quiescent position, the mercury within the housing 63 is collected in the lowest of the two chambers, for instance, the chamber 68, the supply of mercury being such that the level of the pool indicated at 81 is below the xed contact 74, and the electrical circuit between con# tacts 74 and 75 is open. Obviously, at this time there is no mercury in the upper chamber 67, and the contacts 70 and 71 are also electrically disconnected. When the switch vessel 63 is inverted by a suitable mechanism for driving the shaft 66, the mercury tends to ow very slowly through the passageway 69 due to the constriction 69a therein. The level of the mercury in the chamber 68, as indicated at 82, is at this time sulicient to immerse both of the contacts 74 and 75, thus closing the electrical circuit controlled thereby as soon as the shaft 66 is actuated. The contacts 74 and 75 will remain closed for a predetermined interval until the flow of mercury through passageway 69 reduces the level of the mercury in the chamber 68 below that required to maintain contact. After contact between contacts 74 and 75 is severed, the mercury continues to flow through passageway 69 until it is all collected in the chamber 67, which at this time occupies the lowest position. When all of the mercury has been deposited in the chamber 67, the level of the same is still insufficient to close the contacts 70 and 71. The next succeeding actuation of the shaft 66 reverts the switch to the position shown in Fig. 6 and closes the contacts 70 and 71 due to the level of the mercury in chamber 67. These contacts remain closed for a predetermined interval until enough mercury flows through passageway 69 and into the chamber 68 to reduce the level in chamber 67 below the contact 70. When all of the mercury is collected in chamber 68, another cycle of operation has been completed and the switch is ready for the next succeeding actuation of shaft 66 to initiate a new cycle.

in the switch arrangements described thus far, suitable barrier devices were required to insure quick circuit opening. ln another embodiment of the invention, quick break is insured without employing such barriers. Such an embodiment is illustrated in Fig. 7, wherein there is shown a switch 90 which differs from the switch 10, shown in Fig. 4, principally by the provision of means for automatically returning the switch to its normal position only after the timed interval has expired, thus insuring a quick break without the barrier requirement. Specifically, the switch 9i) comprises a housing divided into two separate and independent sections 92 and 93, which are sealed from each other. A pair of xed con tacts 94 and 95 extending through the wall of section 92 of the housing are adapted to be controlled by the ow of a pool of mercury 96 contained within this housing section 92. A barrier like that shown in Fig. 4 may be interposed between the contacts 94 and 95, if desired, although it is not at all necessary, as will become apparent from the following description.

The housing section 93 also contains a pool of mercury which, as previously indicated, is completely isolated from the pool 96 contained within the chamber 92. The section 92 includes a relatively large passageway 98 permitting the free flow of mercury therethrough and a restricted passageway 99 permitting only a small flow of mercury. For the purpose of impeding and controlling the flow of mercury through the restricted passageway 99, this passageway includes a constricted portion 99a having a small opening therein. The passageways 98 and 99 are joined at the bottom by a common mercury receiving well 100, and at the top by a chamber 101.

For the purpose of actuating the switch 99 by bringing the mercury ltl into engagement with the contacts 94 and. 95a', this switch is mounted in any suitable manner as by retaining pins l?? and 104 on a pivotable structure 165, including a frame 106 attached to shaft 107. When the shaft 197 is rotated in a counterclockwise direction, as viewed in Fig. 7, by suitable actuating mechanism, not shown, the switch 90 is rotated until the bottom edge 92a of the section 92 contacts a stationary stop 109 positioned at any desired point in its path of movement. When the switch 90 is rotated in this manner, a portion of the pool of mercury in section 93 of the housing is trapped in the upper chamber 101, and the pool of mercury 96 in section 9?; hows into engagement with the contacts 94 and 95 in order to complete the electrical circuit therebetween. The trapped mercury in the chamber 101 begins to flow through the passageway 99 and into the well 100 at the '10 bottom of section 93 of the housing. When suicient mercury has passed through the opening in the constricted portion 99a of the passageway 99, the weight of the mercury in the well 100 causes a moment of force to be produced which tends to move the switch 90 away from the stop 109 and to rotate the same in a clockwise direction, as viewed in Fig. 7. As soon as the switch 90 is lifted away from the stop 109, the bulk of the mercury in the chamber 101 pours through the large passageway 98 and into the well 100, thus causing the entire switch unit to rotate rapidly and quickly break the electrical circuit between contacts 94 and 95 by moving the mercury 96 in section 92 away from these contacts. The switch 90 then remains in the position assumed after its clockwise rotation until the next succeeding actuation of the shaft 107. Obviously, after each actuation of the shaft, electrical contact between contacts 92 and 93 is maintained for a selected interval determined by the time required for sutcient mercury to ow through passageway 99 to shift the center of gravity of the switch. The separation of the mercury into separate pools for engaging the electrical contacts and for timing the interval during which the contacts are closed has the desirable elect that amalgamation or contamination of the mercury due to contact with metal parts which might lead to the formation of scum does not clog up the constricted portion 99a of the passageway 99. Thus, the timing interval is maintained uniform even after extended use of the switch.

From the foregoing explanation, it is apparent that the present invention provides a sturdy, inexpensively con structed and yet eiciently operating switch which closes its contacts at a selected instant and maintains the same closed until the expiration of a predetermined interval. Such a switch can readily interrupt a current of 20 amperes at 110 volts after a time delay of a half minute or more. Due to the elimination of most of the moving parts of the switch, mechanical failures are practically eliminated, and, as a consequence, useful life of the switch is very long. Furthermore, the actuation of the switch by a uniform force regardless of the amount of manual force applied to the operating mechanism for the switch provides a cycle of operation having a constant duration and at the same time minimizes the possibility of damage to the switch which might result from the application of excessive operating force.

While particular embodiments of the invention have been shown, it will be understood, of course, that the invention is not limited thereto, since many modifications may be made, and it is contemplated by the appended claims to cover any such modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A timing switch for electrically closing a pair of contacts at any initial instant and for maintaining said contacts closed for a definite interval thereafter, comprising a pivotable housing including structure dividing the same into separate enclosed sections, a first of said sections carrying said contacts in spaced apart relationship, a supply of conducting uid within said rst section and adapted to flow into and out of engagement with said contacts to make and break the same, a supply of fluid contained within the second section of said housing, said second section including structure defining a passageway having a constricted portion therein through which the fluid in the second section is adapted to flow and also including structure forming a well offset from the axis about which said housing is pivoted, means for pivoting said housing from its normal position at said initial instant to bring the conducting fluid in the first section into electrical contact with said contacts to make the same and for elevating the uid in said second section to cause the latter to begin to flow through said passageway, the llow of fluid through said passageway and into said well continuing until the weight of fluid in said well is suicient i1 to pivot said housing about its aXis and restore the same to its normal position, at which time electrical contact between said conducting Vfluid and said contacts is broken.

2. In a switch, a pivotable housing, at least one pair of electrical contacts carried by said housing, a barrier member associated with one of said contacts, said barrier including a well in which the associated contact is disposed, and a trough in said barrier connecting said well with the interior of said housing, a supply of conducting fluid contained within said housing, at least a portion of which is adapted to flow into and out of engagement with said contacts in order to electrically vmake and break the same, selectively controlled means for pivoting said housing to control the ow of said uid into or out of engagement with said contacts, and means including a passageway in said housing having a constriction therein for restricting the ow of at least a portion of said fluid for controlling the time interval between the actuation of the means for pivoting said housing and the flow of fluid into or out of engagement with said contacts.

3. Switching apparatus comprising a housing divided into two sections, a plurality of electric ,contact members extending through the wall of said housing into one of said sections, a conducting uid disposed in said one of said sections, means for pivotally mounting said housing so that when said housing is in a predetermined condition of orientation the luid in said one of said sections connects certain ones of said contacts and when the housing is in another condition of orientation the iluid in said one section is disposed so that said certain ones of saidcontacts are mutually disconnected, a liquid in the other of said sections, said other of said sections including a rela tively large passageway for permitting the free flow of liquid therethrough and a restricted passageway for impeding the ow of liquid threthrough, and first and second reservoirs in said housing, said reservoirs being disposed on opposite sides of said restricted passageway and interconnected by said large passageway, said reservoirs being so located that when said liquid is in one of said reservoirs the housing is oriented under the force of gravity in said predetermined condition and when said liquid is in the other of said reservoirs said housing is oriented under the force of gravity in said other condition of orientation.

References Cited in the tile of this patent UNITED STATES PATENTS 1,094,440 Hatfield Apr. 28, 1914 2,026,373 Bush Dec. 31, 1935 2,031,458 Bush Feb. 18, 1936 2,254,710 Reid Sept. 2, 1941 2,295,054 Rudd Sept. 8, 1942 

